Chunk McGowan was a big brawling Irish laborer and Ikey Schoenstein was a druggist. They shared a landlord, Mr. Riddle, and they were both in love with his daughter, Rosy. Chuck wants Rosy to elope with him and she keeps putting him off. He goes to Ikey for a love-philtre to push the maiden along not knowing that Ikey was a silent but nonetheless earnest competitor.
In researching this story I found that among Sidney Porter's (aka O. Henry) many occupations that he'd once been a druggist.